SEMESTER 2025 - SUMMER
04.03.2025
Andreas Trautner
CFTP, IST, University of Lisbon
Electroweak scale hierarchy from conformal and custodial symmetry
I will introduce the idea of "Custodial Naturalness" to explain the origin of the electroweak scale hierarchy. Custodial Naturalness is based on classical scale invariance as well as an extension of the Standard Model (SM) scalar sector custodial symmetry to SO(6). This requires a single new complex scalar field charged under a new U(1) gauge symmetry which partially overlaps with B-L. Classical scale invariance and the high-scale scalar sector custodial symmetry are radiatively broken by quantum effects that generate a new intermediate scale by dimensional transmutation. The little hierarchy problem is solved because the Higgs boson arises as pseudo-Nambu-Goldstone boson of the spontaneously broken SO(6) custodial symmetry. The minimal realization of Custodial Naturalness has the same number of parameters as the SM and predicts testable new physics in the form of a heavy Z' as well as a light but close-to invisible dilaton. Simple extensions furthermore allow to explain neutrino masses and Dark Matter - only in a region of parameter space that can be completely excluded by future colliders.
Slides
18.03.2025
Kodai Sakurai
Tohoku University
Primordial black hole formation by inverted bubble collapse
A primordial black hole (PBH) is one of the promising candidates for dark matter. PBHs can form when significant density perturbations are generated in the early Universe. Various mechanisms for producing overdense regions that lead to PBH formation have been proposed in the literature. Many of these mechanisms postulate that such an overdense region has spherical symmetry; however, in general, deviations from a perfect sphere can occur, making PBH formation nontrivial. In this talk, we discuss a novel mechanism for PBH formation in which the generated overdense region maintains spherical symmetry. We also demonstrate that the observed microlensing events in the OGLE and Subaru HSC data can be explained by applying this new mechanism to extended Higgs models.
Slides
01.04.2025
Werner Porod
Univeristy of Würzburg
Using gauge/gravity duality for strongly interacting models
We use a holographic model of chiral symmetry breaking based on gauge/gravity duality to determine the meson and baryon spectrum of strongly interacting models. We introduce this approach by applying it first to two flavour QCD and then include also flavour effects like different quark masses for three flavour QCD. Moving to Composite Higgs models, we use this approach for different models with varying number of colors and flavours. We will focus in particular on models where we can compare part of our results to related lattice studies.
Slides
15.04.2025
Ayuki Kamada
University of Warsaw
Quantum theory of dark matter scattering
A long-range force between dark matter particles makes significant impacts on dark matter phenomenology. It enhances the annihilation cross section at the late Universe (Sommerfeld enhancement), which affects the prospects for detecting annihilation products (indirect detection experiments). It also leads to a large self-scattering cross section, which forms a significant core in dark matter halos. When the Sommerfeld enhancement factor is significantly large for a certain value of the parameter (resonance), the self-scattering cross section is also resonantly enhanced. In this talk, we first review how the Sommerfeld enhancement factor and self-scattering cross section are usually computed in quantum mechanics. Then, we show that partial-wave unitarity of Sommerfeld-enhanced annihilation cross section is violated on resonance. In the end, we discuss the on-going efforts to restore unitarity.
Slides
29.04.2025
Sreemanti Chakraborti
IPPP Durham
Searching Ultralight Axions with Quantum Technology
In this talk, I will discuss axion-like particles (ALP) as dark matter candidates in the "ultralight mass regime". Starting from the ALP Lagrangian at the UV scale, a consistent QFT treatment is required to obtain interactions at low energy. A plethora of quantum sensor experiments has been designed so far to search for very light ALPs that are particularly sensitive to these effects because they probe large values of the decay constant for which running effects become important. In addition, while linear axion interactions are set by its pseudoscalar nature, quadratic interactions are indistinguishable from scalar interactions. This makes the two types of interactions sensitive to different categories of experiments. I will discuss the reach of various experiments exploiting quantum technology via quantum sensors like atomic clocks, optical interferometers, atom interferometers, etc, and microwave cavity-haloscopes. Lastly, I will touch on the nonlinear behaviour of the ALP field close to the surface of the earth and identify the experiments impacted by this effect.
Slides
13.05.2025
Stefan Lederer
Technische Universität München
Excited bound states and their role in dark matter production
I will discuss the impact of highly excited bound states on the evolution of number densities of new physics particles, focusing on dark matter, in the early Universe. In case of non-Abelian gauge interactions, which source dipole interactions between fundamental particles, highly excited states can prevent the particles from freezing, supporting a continuous depletion in the regime consistent with perturbativity and unitarity. Unitarity violation does in fact arise systematically in controlled leading order bound state formation calculations, that is, even for arbitrary small interaction strengths when sufficiently highly excited states become relevant at low velocities. Novel analytic expressions for bound state formation allow to accurately compute the freeze-out dynamics down to very low temperatures. I will highlight the importance of bound states to dark SU(N) sectors. For a more concrete dark matter model, I will focus on a colored and charged t-channel mediator model in the regime of superWIMP production. Here, excited states render the mediator depletion efficient all the way until its decay, introducing a dependence of the dark matter density on the mediator lifetime as a novel feature.
Slides
27.05.2025
Aditya Batra
CFTP, University of Lisbon
10.06.2025
Dominik Stöckinger
TU Dresden